Marine seismology companies invest heavily in the development of marine seismic surveying equipment and seismic data processing techniques in order to obtain accurate, high-resolution seismic images of subterranean formations located beneath a body of water. High-resolution seismic images of a subterranean formation are used to determine the structure of subterranean formations, discover petroleum reservoirs, and monitor petroleum reservoirs during production. A typical marine seismic survey is carried out with a survey vessel that tows one or two seismic sources and a number of streamers through the body of water. The survey vessel contains seismic acquisition equipment, such as navigation control, seismic source control, seismic receiver control, and recording equipment. The seismic source control controls activation of the one or two seismic sources at selected times or locations. A seismic source typically comprises an array of source elements, such as air guns, that are simultaneously activated to produce an acoustic impulse. The acoustic impulse is a sound wave that travels down through the water and into a subterranean formation. At each interface between different types of rock and sediment, a portion of the sound wave is refracted, a portion of the sound wave is transmitted, and another portion is reflected back into the body of water to propagate toward the water surface. The streamers are elongated cable-like structures that are towed behind the survey vessel in the direction the survey vessel is traveling (i.e., sail-line direction) and are arranged substantially parallel to one another in the direction perpendicular to the sail-line direction. The streamers collectively form a seismic data acquisition surface. Each streamer includes a number of seismic receivers or sensors that detect pressure and/or particle motion wavefields of the sound waves reflected back into the water from the subterranean formation. The recorded pressure and/or particle motion wavefields are processed to produce seismic images of the subterranean formation.
In order to reduce the cost per square kilometer of three-dimensional seismic data acquisition and maximize the sub-surface area surveyed per sail line, marine seismology companies often deploy longer streamers with greater separation between the streamers as compared to more traditional marine surveys. For example, a traditional marine seismic survey may be carried out with ten 6,000 m long streamers separated by about 75 m By contrast, the acquisition time of a marine survey can be lower with sixteen 7,000 m long streamers separated by 100 m, and still lower with twelve 8,000 m long streamers separated by 150 m, and even lower with ten 10,000 m long streamers separated by 200 m. In terms of overall marine survey productivity these large streamer separations reduce data acquisition times from between 35% to 50%, which translates into a significant savings in time and costs.
However, efforts to lower cost by increasing streamer length and distances between streamers may have a downside in that the spatial resolution of the seismic data collected is typically lower than the seismic data collected in surveys carried out with shorter, more closely separated streamers for the following reasons. As the lengths of streamers are increased, the seismic recording time intervals between seismic source activations is increased in order to capture returning signals from longer source-receiver offsets. The longer recording time intervals necessitate more time between activations of the seismic sources and, therefore, a larger sail-line distance is traveled between activations of the seismic sources. In addition, as streamer separation increases from 100 m, to 150 m, to 200 m, cross-line sampling between streamers leads to spatial aliasing in the direction perpendicular to the sail-line direction. As a result, traditional dual seismic source acquisition techniques combined with longer streamer lengths and larger distances between streamers leads to a decrease in overall seismic data density, a decrease in the number of seismic source activations used to acoustically illuminate the subterranean formation, and increased spatial aliasing perpendicular to the sail-line direction. These factors impact the ability to adequately sample reflected wavefields from the subterranean formation, remove coherent noise, and provide sufficient spatial sampling to image complex subterranean geological structures.